Date Published: May 9, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Wei Gao, Xiaofei Yin, Tiezhu Mi, Yiran Zhang, Faxiang Lin, Bin Han, Xilong Zhao, Xiao Luan, Zhisong Cui, Li Zheng.
In 2013, the “Qingdao oil pipeline explosion” released an estimated 2000 tons of oil into the environment. Sediment samples were collected from ten sites in Jiaozhou Bay and Shilaoren Beach to evaluate the influence of the spilled oil on the benthic environment 3 years after the oil spill accident. The compositions of oil, bacterial diversity and biotoxicity were examined in this study. The results showed that the concentration of total petroleum hydrocarbons (TPHs) peaked near the oil leak point and gradually decreased along the coastline, ranging from 21.5 to 133.2 μg/g. The distribution of polycyclic aromatic hydrocarbons (PAHs) was correlated with TPH, and naphthalenes were dominant in the 20 detected PAHs. The bacterial diversities in seriously polluted and slightly polluted sediments were completely different. As degrading bacteria, Alcanivorax and Lutibacter were the main genera at the oil-polluted sites. The analysis of biotoxicity by the luminescent bacteria method showed great differences among the polluted sites, the control site in Jiaozhou Bay, and the non-polluted site outside of Jiaozhou Bay. The biotoxicity also peaked at the site near the oil leak point. These results indicate that the oil spill that occurred 3 years ago still affects the environment and impacts the bacterial communities in the sediments.
On Nov 22nd, 2013, an oil pipeline exploded in Huang Dao, Qingdao City, China. The crude oil spilled into the sea through the municipal pipelines. An estimated 2.5 km of shoreline was seriously polluted by the oil spill. To mitigate the impact of the oil, dispersants were applied to surface waters around the leak point. The use of the dispersants was meant to promote the deposition of the oil to the sea floor (Gong et al. 2014). Meanwhile, the harbour (near the leak point in Jiaozhou Bay-an inner sea) might prevent the oil from reaching the open sea. The special hydrological characteristics of these sites might keep the oil near the shoreline where it could persist for a long time. Therefore, the spilled oil would have a different impact on the benthic environment.
Offshore oil well blowouts or pipeline ruptures cause large amounts of oil to spill into marine environments, such as the Deepwater Horizon oil spill, the Bohai 19-3 oil spill and the Huangdao 11.22 oil pipeline explosion. Oil dispersants were widely applied in the marine oil removal process (Kleindienst et al. 2015). The dispersants lower the oil–water interfacial tension and break oil slicks into fine droplets. These dispersed oils may aggregate with suspended particulate material (SPM), such as clay minerals or organic matter, to form oil-SPM aggregates (OSAs) that get trapped on the bottom substrates in nearshore waters (Gong et al. 2014). It was estimated that 65% of released oil might form OSAs. This may result in serious pollution to the benthic environment because of the large amount of the spilled oil associated with each event. Studies have shown that oil including relatively labile low-molecular-weight n-alkanes, aromatics and BTEX (benzene, toluene, ethylbenzene, and p-, m-, and o-xylenes) remained in sediments 1 year after a spill (Liu et al. 2012). In our study, TPH was detected in all sediments from the nine sampling sites in Jiaozhou Bay. Five of the nine sites were moderately polluted according to Massoud’s et al. standard (1996). The TPH concentration of site A3 (near the oil leaking point) was close to a heavily polluted value (i.e., > 200 μg/g). In a previous study of Jiaozhou Bay, the concentrations of PAHs ranged from 1242.21 to 29,558.13 ng/g in sediments (Xue 2009). In the present study, the concentrations of PAHs were within this range at most sites. However, the concentration at site A3 was much higher than the average value found in Jiaozhou Bay. This means there was an exogenous input of PAHs to this site. On the other hand, the previous studies showed that the PAHs were mainly composed of high-molecular-weight components. In our study, low-ring PAHs accounted for a large proportion. Another study in Daya Bay showed that the increase in naphthalene content may be due to oil pollution, and this supports that the contamination of the sediments in Jiaozhou Bay was from crude oil (Sun et al. 2016).